Digital camera image sensor positioning apparatus including a non-coherent light interferometer

ABSTRACT

An optical probe apparatus and method for determining a position of an image sensor within a digital camera relative to a reference surface. The apparatus includes an optical probe assembly removably mountable to the digital camera. A non-coherent light interferometer in communication with the optical probe assembly is utilized to determine a depth from a reference surface to the image sensor and optical probe assembly.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is related to commonly assigned U.S. Ser. No.08/408,871, titled ASSOCIATED INTERFEROMETRIC MEASUREMENT APPARATUS FORDETERMINING A PHYSICAL PROPERTY OF AN OBJECT, by Marcus et al, filed onMar. 22, 1995, and issued as U.S. Pat. No. 5,659,392 and to commonlyassigned U.S. Ser. No. 08/408,770, titled ASSOCIATED INTERFEROMETRICMEASUREMENT METHOD FOR DETERMINING A PHYSICAL PROPERTY OF AN OBJECT, byMarcus et al, filed on Mar. 22, 1995, and issued as U.S. Pat. No.5,596,409, and to commonly assigned U.S. Ser. No. 08/755,072, titledMETHOD FOR DETERMINING A POSITION OF AN IMAGE SENSOR IN A DIGITALCAMERA, by Marcus et al, filed on Nov. 22, 1996.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is related to commonly assigned U.S. Ser. No.08/408,871, titled ASSOCIATED INTERFEROMETRIC MEASUREMENT APPARATUS FORDETERMINING A PHYSICAL PROPERTY OF AN OBJECT, by Marcus et al, filed onMar. 22, 1995, and issued as U.S. Pat. No. 5,659,392 and to commonlyassigned U.S. Ser. No. 08/408,770, titled ASSOCIATED INTERFEROMETRICMEASUREMENT METHOD FOR DETERMINING A PHYSICAL PROPERTY OF AN OBJECT, byMarcus et al, filed on Mar. 22, 1995, and issued as U.S. Pat. No.5,596,409, and to commonly assigned U.S. Ser. No. 08/755,072, titledMETHOD FOR DETERMINING A POSITION OF AN IMAGE SENSOR IN A DIGITALCAMERA, by Marcus et al, filed on Nov. 22, 1996.

FIELD OF THE INVENTION

The invention relates to an apparatus and method for determining aposition of an image sensor in a digital camera, whereby the imagesensor can be positioned to provide a focused image.

BACKGROUND OF THE INVENTION

In a typical digital camera, an image beam is directed through a lensand onto an imager or image sensor, for example a CCD (Charge CoupledDevice), comprised of an array of sensing elements. The lens and the CCDneed to be properly positioned relative to each other within the digitalcamera to provide a focused image. In order to properly position theCCD, the position of the CCD needs to be determined. Such a position canbe determined relative to a reference surface or reference plane.

A Coordinate Measuring Machine (CMM) is an example of an apparatusemployed to determine the position of an object relative to a referenceplane. Typically, the object is retained in a suitable holder on anoptical bench. In one method to determine the position of an object,three points on a reference plane approximately 120 degrees apart aremeasured to define the reference plane; the coordinates of the threepoints being tracked in the x, y and z locations. A point on the objectis then measured relative to the reference plane, and the distance fromthe reference plane is calculated. Typical coordinate measurementmachines include contact probes for contacting each of the pointsdefining the reference plane and the object, such as those described inU.S. Pat. No. 5,428,446 (Ziegart et al.), U.S Pat. No. 5,446,545(Taylor) and U.S. Pat. No. 4,929,082 (Webber). These references includeinterferometers which monitor the displacement of the machine axes.Non-contact methods include optical triangulation as described in U.SPat. No. 4,373,804 (Pryor) and U.S. Pat. No. 5,510,625 (Pryor).

While such apparatus and methods may have achieved a certain level ofsuccess, the apparatus are not readily transportable and simple to use.Further, the method is time consuming and often dependent on the skillof the operator.

Accordingly, a need continues to exist for an apparatus and method fordetermining the position of an image sensor in a digital camera. Theapparatus needs to be robust, transportable, simple to use, and readilymounted and dismounted to the digital camera. The method must be fast,provide objective results independent of the operator, and provideaccurate consistent results.

SUMMARY OF THE INVENTION

An object of the invention is to provide an apparatus and method fordetermining a position of an image sensor in a digital camera.

Another object of the invention is to provide such an apparatus which isrobust, transportable, simple to use, and readily mounted to the digitalcamera.

Yet another object of the invention is to provide such an apparatus andmethod for determining the degree of flatness of an image sensor.

A further object of the invention is to provide such an apparatus andmethod for determining the parallelism of a plane of an image sensorrelative to a reference surface.

Still another object of the invention is to provide such a method whichis fast, provides objective results independent of the operator, andprovides accurate, consistent results.

These objects are given only by way of illustrative example. Thus, otherdesirable objectives and advantages inherently achieved by the disclosedinvention may occur or become apparent to those skilled in the art. Theinvention is defined by the appended claims.

According to one aspect of the invention, there is provided an apparatusfor determining a position of an image sensor in a digital camerarelative to a reference surface on the digital camera. The image sensorincludes an imager plane and an optically transparent plate having afront surface and a back surface, with the plate being spaced from theimager plane. The apparatus includes an optical probe assembly which isremovably mountable to the digital camera and lockable in apredetermined orientation relative to the digital camera. The opticalprobe assembly includes both an optical probe, and a pellicle securelymounted relative to the optical probe, such that the pellicle isdisposed intermediate the reference surface and the imager plane. Thepellicle is disposed at a first depth from the reference surface whenthe optical probe is in the locked orientation, and the opticallytransparent plate is disposed intermediate the imager plane and thepellicle. The apparatus further includes a non-coherent lightinterferometer and a non-coherent light source in communication with theoptical probe by means of an optical coupler. In addition, means areprovided for determining (i) a second depth from the reference surfaceto the optically transparent plate front surface, (ii) an opticalthickness of the optically transparent plate, and (iii) a third depthfrom the optically transparent plate back surface to the imager plane.

According to another aspect of the apparatus of the invention, forpositioning such an image sensor in a digital camera relative to anin-focus position, the apparatus further includes translation means foraligning the imager plane at the in-focus position.

According to yet a further aspect of the apparatus of the invention,there is provided an apparatus for determining a position of an imagesensor mounted in a digital camera relative to a reference surface onthe digital camera. Such an apparatus includes an optical probe assemblywhich is removably mountable to the digital camera and lockable in apredetermined orientation relative to the digital camera. The opticalprobe assembly includes a plurality of optical probes, and a pelliclesecurely mounted relative to each of the plurality of optical probes,whereby the pellicle is disposed intermediate the reference surface andthe imager plane. As such, the pellicle is disposed at a first depthfrom the reference surface when the optical probes are in the lockedorientation, and the optically transparent plate is disposedintermediate the imager plane and the pellicle. The apparatus furtherincludes a non-coherent light interferometer and a non-coherent lightsource in communication with the optical probes by means of an opticalcoupler; an optical switching means; and means for determining, for eachof the plurality of optical probes, (i) a second depth from thereference surface to the optically transparent plate front surface, (ii)an optical thickness of the optically transparent plate, and (iii) athird depth from the optically transparent plate back surface to theimager plane.

According to yet a further aspect of the invention, there is provide anapparatus for determining a position of an image sensor mounted in adigital camera relative to a reference surface on the digital camerawherein the apparatus includes an optical probe assembly removablymountable to the digital camera and lockable in a predeterminedorientation relative to the digital camera. The optical probe assemblyincludes both an optical probe, and a pellicle securely mounted relativeto the optical probe. The pellicle is disposed intermediate thereference surface and the imager plane, and disposed at a first depthfrom the reference surface when the optical probe is in the lockedorientation. The optically transparent plate is disposed intermediatethe imager plane and the pellicle. The apparatus further includes anon-coherent light interferometer and a non-coherent light source incommunication with the optical probe by means of an optical coupler;translation means for moving the optical probe along an axis normal tothe reference surface to provide a plurality of measurement locations;and means for determining, at each of the plurality of measurementlocations, (i) a second depth from the reference surface to theoptically transparent plate front surface, (ii) an optical thickness ofthe optically transparent plate, and (iii) a third depth from theoptically transparent plate back surface to the imager plane.

According to yet another aspect of the invention, there is provide anapparatus for determining whether an image sensor mounted in a digitalcamera is parallel relative to a reference surface. A further aspect ofthe invention provides an apparatus for determining the degree offlatness of an image sensor mounted in a digital camera.

The present invention provides an apparatus and method for determiningthe position of an image sensor in a digital camera. The apparatus isrobust, transportable, simple to use, and readily mounted to the digitalcamera. The method is fast, provides objective results independent ofthe operator, and provides accurate and consistent results.

BRIEF DESCRIPTION OF THE DRAWING

The foregoing and other objects, features, and advantages of theinvention will be apparent from the following more particulardescription of the preferred embodiments of the invention, asillustrated in the accompanying drawings.

FIG. 1 shows a lens mounted within a camera body.

FIG. 2 shows a CCD mounted within a camera body.

FIG. 3 shows a non-coherent light interferometric measurement apparatusaccording to the present invention.

FIG. 4(a) shows a cross-sectional view of the optical probe assembly ofFIG. 3 while FIG. 4(b) shows an exploded view of the optical probeassembly of FIG. 3.

FIG. 5 shows a schematic view of the relationship of the optical probeassembly and the CCD when the optical probe assembly is mounted to thecamera body.

FIG. 6 shows a first embodiment of a non-coherent light interferometricmeasurement apparatus in accordance with the present invention.

FIG. 7 shows a second embodiment of a non-coherent light interferometricmeasurement apparatus in accordance with the present invention.

FIG. 8 shows reflections corresponding to the schematic view illustratedin FIG. 5.

FIG. 9 shows an interferograin obtained with the present invention andcorresponding to the reflections illustrated in FIG. 8.

FIG. 10 shows a series of reflections observed as the optical path delayelement is moved in accordance with the present invention.

FIG. 11 shows a non-coherent light interferometer of FIG. 3 having astandard mode configuration in accordance with the present invention.

FIG. 12 shows a flow chart illustrating one method according to thepresent invention utilizing an autocorrelation mode configuration of anon-coherent light interferometer.

FIG. 13 shows a flow chart illustrating another method according to thepresent invention utilizing an autocorrelation mode configuration of anon-coherent light interferometer.

FIG. 14 shows a flow chart illustrating a further method according tothe present invention utilizing a standard mode configuration of anon-coherent light interferometer.

FIG. 15 shows a multi-point non-coherent light interferometricmeasurement apparatus according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The following is a detailed description of the preferred embodiments ofthe invention, reference being made to the drawings in which the samereference numerals identify the same elements of structure in each ofthe several figures.

Referring to FIG. 1, a lens 12 is mounted to a camera body 10 by meansof a lens mount 14. The distance at which lens 12 focuses light in thecamera body is referred to as the focal depth F_(depth) of the lens inair, measured along the z-axis. The focal depth F_(depth) can bedetermined by means known to those skilled in the art. In a conventionalcamera employing photographic film 13 as the image media, the film ispositioned at the focal depth F_(depth) of the lens. FIG. 1 illustratesfilm 13 positioned at the focal depth of the lens, to provide a focusedimage. Means (not shown) such as film rails, may be employed to positionfilm 13 at the focal depth F_(depth). Hereinafter, the terminology"in-focus position" refers to a position at which an imaging media ispositioned to provide an in-focus image.

Referring to FIG. 2, in a digital camera body 15, lens 12 is typicallymounted to the digital camera by means of lens mount 14. An image sensor16 is employed as the imaging media. Image sensor 16 comprises an imagerplane 18 referring to an active surface of the image sensor. Imagesensor 16 generally further comprises an optically transparent plate 20having an index of refraction n. Imager plane 18 is spaced from plate 20such that a gap or interstice 22 is interposed intermediate the imagerplane and the plate. Typically, the imager plane and the transparentplate are hermetically sealed with a defined interstice 22.

As indicated above with regard to a conventional camera, the distance atwhich lens 12 focuses light is referred to as the focal depth F_(depth)of the lens. However, in a digital camera, the presence of plate 20(disposed intermediate the lens and the image sensor) affects thein-focus position. Accordingly, an in-focus position F₁ for imager plane18, taking into account the presence of plate 20, is determined by:##EQU1## t being the thickness of plate 20 and n being the index ofrefraction of plate 20.

FIG. 3 provides a general illustration of a non-coherent lightinterferometric measurement apparatus 21 according to the presentinvention for determining the position of image sensor 16 relative to areference surface on the digital camera. The apparatus allows a user toverify that the position of imager plane 18 is within a desiredtolerance. If the position of imager plane 18 is outside the desiredtolerance, the image sensor can be re-positioned to move imager plane 18to a desired position, such as the in-focus position F_(I).

Lens 12 is generally mounted to digital camera body 15 by lens mount 14.Conventional means (not shown) are known to facilitate mounting of thelens to the camera body. Such means may include: a screw lens mountwherein screw threads allows installation of the lens to the camerabody; a bayonet lens mount wherein the lens slips over a mating flangeon the camera body with a twist of about 45 degrees; or a breechlocklens mount wherein a knurled collar on the back of the lens fits over amating flange on the camera body. To secure the mounting, the lens mountmay include a locking means to lock the lens to the lens mount.Similarly, to unlock the lens from the lens mount, an unlocking meansmay be included.

In the present invention, to determine the position of imager plane 18,lens 12 is removed from digital camera body 15. Since lens 12 isremoved, the position of imager plane 18 is determined relative to areference surface on digital camera body 15. While various surfaces(including, but not limited to, components of the digital camera body)may be used as a reference surface, for ease of discussion, lens mount14 will provide the reference surface. Therefore, the position of imagerplane 18 will be discussed as being determined relative to lens mount14.

Referring to FIG. 3, an optical probe assembly 24 is removably mountedto lens mount 14 to securely, but temporarily, attach optical probeassembly 24 to digital camera body 15. Preferably, optical probeassembly 24 incorporates the means to allow the assembly to be mountedto digital camera body 15 by means of the bayonet lens mount wherein theassembly would slip over a mating flange on the camera body with a twistof about 45 degrees. To temporarily secure the mounting, a locking means23, for example a spring loaded locking pin, locks optical probeassembly 24 to lens mount 14. To unlock optical probe assembly 24 fromlens mount 14, an unlocking means 25 such as a spring loaded releasepin, is employed thereby allowing optical probe assembly 24 to bereadily released from digital camera body 15. Note that such lockingmeans 23 and unlocking means 25 may optionally be employed to lock andunlock, respectively, lens 12 to lens mount 14.

Optical probe assembly 24 includes a single mode optical fiber cable 26coupled to a 1×2 optical coupler 28. Preferably, connectors andpatchcords (not shown) of variable length (preferably patchcords whichterminate with a low back reflection connector such an FC connector) aredisposed between optical coupler 28 and optical probe assembly 24 topermit portability for the apparatus and to permit remote locationmounting. A non-coherent light source 30, such as an LED (Light EmittingDiode), is coupled into a single mode fiber 32 and passes through 1×2optical coupler 28. A suitable non-coherent light source 30 is a high267 bandwidth (approximately 40-120 nm) 1300 nm center wavelength LEDhaving 1-10 microwatts of coupled power.

Generally, light from non-coherent light source 30 travels along opticalfiber 26, transmitted through optical probe assembly 24, and is incidenton image sensor 16. The light is reflected from each of the surface ofimage sensor 16, and passes back through optical probe assembly 24 intooptical fiber 26. The reflected light then passes through 1×2 opticalcoupler 28 into an optical fiber 34, which is introduced into anon-coherent light interferometer 36. Preferably, interferometer 36 isof a Michelson configuration, though a non-Michelson configuration hasbeen found suitable. Associated with non-coherent light interferometer36 is a computing means 38, such a computer, for controlling,collecting, manipulating, analyzing, and storing data.

Optical probe assembly 24 is further illustrated in FIGS. 4(a) and 4(b).Optical probe assembly 24 comprises a probe mounting surface 40, anoptical probe 42 such as a collimating lens or fiber collimator, probeassembly mounting means 44, probe housing 43 having a probe assemblygripping means 45, a probe recess 46 (not shown), a pellicle 48 disposedat a predetermined depth P_(depth) from probe mounting surface 40, and apellicle mount 49.

Probe assembly mounting means 44 allows optical probe assembly 24 tomate with a camera body wherein optical probe assembly 24 is removablymounted to camera body 15 in a predetermined orientation. As notedabove, probe assembly mounting means 44 preferably incorporates theconventional bayonet lens mount wherein optical probe assembly 24 wouldslip over a mating flange on the camera body with a twist of about 45degrees. As such, an operator would grasp optical probe assembly 24 bygripping means 45, and mount the optical probe assembly 24 to camerabody 15 by positioning optical probe assembly 24 such that probemounting surface 40 abuts lens mount 14. Optical probe assembly 24 wouldthen be rotated (for example, by approximately 45 degrees) to disposelocking means 23 into recess 46, thereby locking optical probe assembly24 to lens mount 14 in a predetermined orientation. In a preferredpredetermined orientation, probe mounting surface 40 abuts lens mount 14(i.e., the reference surface) to provide a predetermined depth ofpellicle 48 from lens mount 14. The plane defined by abutting probemounting surface 40 and lens mount 14 will hereinafter be referred to asReference Plane A.

To release optical probe assembly 24 from camera body 15, an operatorwould grasp optical probe assembly 24 by gripping means 45, and depressunlocking means 25 to release locking means 23 from probe recess 46. Ifthe conventional bayonet lens mount is utilized (wherein optical probeassembly 24 mounts to the camera body with a twist of about 45 degrees),optical probe assembly 24 can be rotated in an opposite direction (ofapproximately 45 degrees) to dismount the assembly from the camera body.

Pellicle 48 is comprised of an optically transparent material which issufficiently thin so as to not affect the focal depth measurement. Asuitable pellicle can be made of a polyester film material ofapproximately 1.5 μm. Means are provided for securely mounting thepellicle to optical probe assembly 24. For example, as illustrated, anO-ring 50 held in an O-ring groove provides secure mounting to pelliclemount 49. Other means may be known, such as setting pellicle 48 in placewith a suitable adhesive. Pellicle mount 49 predeterminedly disposespellicle 48 from probe mounting surface 40. A suitable pellicle mount 49includes an open aperture of approximately 0.5 inches in diameter and anouter diameter of approximately 0.75 inches.

As indicated above, optical probe assembly 24 provides parallelcollimated light to image sensor 16 when mounted in camera body 15, andcollect light reflected back from image sensor 16. Accordingly,referring now to FIG. 4(b), optical probe assembly 24 includes fibercollimator 42, an optional fiber collimator collar 92, an adjustmentcollar 94, at least one adjustment means 96 (for example, a screw), aball pivot 98, a ball pivot receiving plate 100 having an opening 102 toreceive ball pivot 98, a mounting plate 104, an optional fibercollimator collar mounting means 106, at least one ball pivot receivingplate mounting means 108 (for example, a screw), and at least oneoptical probe assembly means 110. In the preferred embodiment, fibercollimator 42 is an active optical element including a single mode fiberpigtailed, quarter-pitch Gradient index (GRIN) lens assembly. A suitablefiber collimator 42 is a Dicon Fiber collimator Part Number FC-9-1.3FC-3.0-L. Such a fiber collimator includes a lens having a beam diameterof about 0.45 mm and a beam divergence of less than 0.25 degrees.

If optional fiber collimator collar 92 is employed, it surrounds fibercollimator 42 and is securely mounted by optional fiber collimatormounting means 106. Such a suitable mounting means 106 is a 2-56 screw.Fiber collimator 42, with collar 92 securely mounted, is inserted into arecess 112 in adjustment collar 94. As represented in FIG. 4(b), theleft-most end of fiber collimator 42 is inserted into rotatable ballpivot 98. Ball pivot 98, together with fiber collimator 42 attached, isinserted into opening 102 of ball pivot receiving plate 100. Adjustmentcollar 94 is then mounted to ball pivot receiver plate 100 using collarmounting screws (not shown). Adjustment means 96 allow adjustment ofadjustment collar 94 to provide orientation adjustment capability offiber collimator 42. Suitable adjustment means 96 is a 0-80 screw. Theseadjustment means 96 preferably contact a flat surface orientedapproximately 120 degrees apart on fiber collimator collar 92. Ifoptional fiber collimator is not employed, adjustment means 96 contactthe outer surface of fiber collimator 42.

Ball pivot receiver plate 100 is fastened and centered with respect tomounting plate 104 by mounting means 108, thereby locking ball pivot 98in position yet allowing free rotation of fiber collimator 42's opticalaxis by means of adjustment means 96. When assembly is complete,orientation of fiber collimator 42 is preferably performed by means ofthree 120 degree oriented adjustment screws 96. Adjustment is performedwith optical probe assembly 24 mounted in the camera body. Adjustmentsare made until the non-coherent light interference signal fromnon-coherent light interferometer 36 is optimized. This occurs when theoptical axis of fiber collimator 42 is normal to the reference surfaceof the camera body.

Adjustment means 96 are intentionally not readily accessible oncegripping means 45 is attached to the assembly so that furtheradjustments can not be readily made to fiber collimator 42 during ameasurement cycle. Rather, gripping means 45 is attached to opticalprobe assembly 24 by optical probe assembly means 110. In a preferredembodiment, three access holes (one illustrated as element 116 in FIG.4(b)) in probe housing 43 are provided to pennit fine-tuning adjustmentsto fiber collimator 42 via screws 96, if needed. During typical usage,fiber collimator 42 is positioned approximately at the plane of probemounting surface 40 (i.e., the reference surface). During assembly,fiber collimator 42 is adjusted such that maximum signals from pellicle48 are provided when connected to the non-coherent light interferometer.In a preferred embodiment, when mounted in camera body 15, pellicle 48is mounted approximately 40 mm from lens mount 14 with a tight tolerance(of about +/-2 5 microns). Hereinafter, for ease of discussion, acollimating lens orientation and locking means 114 will comprise fibercollimator collar 92 (optional), adjustment collar 94, adjustment means96, ball pivot 98, ball pivot receiving plate 100, opening 102, fibercollimator collar mounting means 106 (optional), collar mounting screws(not shown), and recess 112.

With optical probe assembly 24 mounted to digital camera body 15, theorientation of optical probe 42 and image sensor 16 are as illustratedin FIG. 5. Pellicle 48 is disposed at a predetermined depth P_(depth)from probe mounting surface 40 and, accordingly, lens mount 14 (i.e.,the reference surface positioned at Reference Plane A). The depth frompellicle 48 to a front surface 52 of transparent plate 20 is referred toas PG_(depth), while the depth from pelicle 48 to a back surface 54 oftransparent plate 20 to imager plane 18 is referred to as GS_(depth).Accordingly, the actual depth of D_(actual) imager plane 18 relative tothe reference surface (i.e., lens mount 14 at Reference Plane A) is:

    D.sub.actual =P.sub.depth +PG.sub.depth +t+GS.sub.depth    (Equation 3)

where P_(depth) is the predetermined depth from Reference Plane A topellicle 48; PG_(depth) is the depth from pellicle 48 to front surface52; GS_(depth), is the depth from back surface 54 to imager plane 18;and t is the thickness of transparent plate 20;

The corresponding total optical depth D_(optical) from pellicle 48relative to the reference surface (i.e., lens mount 14 at ReferencePlane A) is given by the equation:

    D.sub.optical =P.sub.depth +PG.sub.depth +nt+GS.sub.depth  (Equation 4)

where n is the index of refraction of plate 20.

Substituting Equation 3 into Equation 4 results in:

    D.sub.actual =D.sub.optical -nt+t=D.sub.optical -t(n-1)    (Equation 5)

Accordingly, the difference between where imager plane 18 is actuallypositioned (i.e., D_(actual)) and the desired position, for example thein-focus position F_(I), is referred to as the difference in focus D_(F):

    D.sub.F =F.sub.I -D.sub.actual                             (Equation 6)

With the optical probe assembly locked to the digital camera in apredetermined orientation whereby the pellicle is disposed at a knownreference depth relative to the reference surface, non-coherent lightinterferometry can be utilized to determine (i) the depth from thereference surface to the front surface of the optically transparentplate, (ii) the optical thickness of the optically transparent plate,and (iii) the depth from the back surface of the optically transparentplate to the image sensor. From this information, the position of imagerplane 18 relative to the reference surface can be determined.

The depth D_(RF) from the reference surface to front surface 52 of plate20 is determined from the relationship:

    D.sub.RF =P.sub.depth +PG.sub.depth                        (Equation 7)

The value P_(depth) is a predetermined value, and the value ofPG_(depth) is measured using the apparatus of the present invention.

FIG. 6 illustrates non-coherent light interferometric measurementapparatus 21 having an optional coherent light interferometer 55 inmechanical association with non-coherent light interferometer 36 in anautocorrelation mode configuration. The autocorrelation modeconfiguration allows the interference spectrum from image sensor 16 tobe independent of the length of fiber disposed between imager sensor 16and non-coherent interferometer 36. Applicants note that single modeoptical fibers up to 10 km in length have been successfully utilizedbetween optical probe assembly 24 and non-coherent light interferometer36 without adverse affect to the resolution of the measurements.

As illustrated in FIG. 6, non-coherent light interferometric measurementapparatus 21 includes non-coherent light interferometer 36, optionalcoherent light interferometer 55, optical probe assembly 24, computer38, and various electronics for signal processing and motor control.

While non-coherent light interferometer 36 can be of a standard modeconfiguration (described below), preferably, non-coherent lightinterferometer 36 is of an autocorrelation mode as illustrated in FIG.6. The autocorrelation mode of non-coherent light interferometer 36transforms a series of non-coherent light constructive interferencepeaks occurring at optical interfaces in the digital camera body todistances from a central autocorrelation peak.

Still referring to FIG. 6, coherent light interferometer 55 provides aknown displacement profile as a function of time. Coherent lightinterferometer 55 includes a coherent light source 56, preferably a HeNelaser, emitting a collimated coherent light signal which is split by asplitting means 58, such as a beam splitter 58, into first and secondcoherent light signals of approximately equal intensity. The firstcoherent light signal is incident on a stationarily mountedretroreflector 60, while the second coherent light signal is incidentonto a movable optical element, such as a retroreflector 62. The firstand second coherent light signals are retro-reflected back to beamsplitter 58 where they recombine and interfere with each other. Thisrecombined, coherent light interference signal is detected by aphotodetector 64 which is fed into and processed by signal processingelectronics 65 and sent to computer 38. The coherent light signal isperiodic, with a constant amplitude and provides constant distanceinterval data acquisition sampling capability. Accordingly, coherentlight interferometer 55 monitors the motion of retroreflector 62; theposition of retroreflector 62 being controlled by a common variable pathdelay element 80.

Non-coherent light source 30 emits a non-coherent light signal alongsingle mode fiber 32 which passes through 1×2 optical coupler 28 tooptical probe assembly 24. Within the optical probe assembly, a portionof the light signal is transmitted through the pellicle and applied toimage sensor 16 positioned within camera body 15. A portion of the lightsignal is reflected by the pellicle, the front surface 52 of plate 20,the back surface 54 of plate 20, and imager plane 18. The light fromnon-coherent light source 30, which is reflected from image sensor 16and pellicle 48, is collected by optical probe assembly 24 and passesthrough optical coupler 28 into optical fiber 34 to be introduced intonon-coherent light interferometer 36.

The signal passing through optical fiber 34 (herein called the objectsignal) is split into first and second non-coherent light signals at 2×2optical coupler 66. The first non-coherent light signal is directedalong a single mode optical fiber 68 to a stationary reference reflector70 through a collimating applying and collecting means 72.Alternatively, single mode optical fiber 68 can be terminated with anormal cleaved mirrored surface at its tip (not shown) in place ofcollimating applying and collecting means 72 and stationary referencereflector 70. A portion of the first non-coherent light signal isreflected back from stationary reference reflector 70 into collimatingapplying and collecting means 72, and is coupled back into single modeoptical fiber 68. This signal is referred to as the reference signal.The second non-coherent light signal, traveling along single modeoptical fiber 74, is incident on collimating applying and collectingmeans 76, which collimates the second non-coherent light signal.Collimating applying and collecting means 76 applies the secondnon-coherent light signal to a mirror 78 mounted onto retroreflector 62,of a common variable optical path delay element 80. Common variableoptical path delay element 80 is mounted for precision movement by amotor 82 in a direction shown by arrow A. A portion of the secondnon-coherent light signal is reflected back from mirror 78 intocollimating applying and collecting means 76 and is coupled back intosingle mode optical fiber 74, forming a delay signal. The optical pathfrom 2×2 optical coupler 66 to stationary reference reflector 70 andback to 2×2 optical coupler 66 is defined as the optical path length ofthe stationary reference branch of non-coherent light interferometer 36.

While alternative configurations for variable optical path delay element80 may be known to those skilled in the art, preferably, variableoptical path delay element 80 includes a prism retroreflector and amirror mounted on the diaphragm cone of a moving-coil loudspeaker; themirror being mounted on a portion of the surface of the prismretroreflector. Therefore, as the loudspeaker cone moves to the left (asillustrated in FIG. 6), the optical path lengths of non-coherent lightsource 30 and coherent light source 56 increases by the same amount.Conversely, the optical path lengths of non-coherent light source 26 andcoherent light source 56 decreases by the same amount as the loudspeakercone moves to the right (as illustrated in FIG. 6). The optical pathlength of common variable optical path delay element 80 is preferablyvaried using a motor drive control electronic module 84 comprising afunction generator and power amplifier, thereby controlling the currentto the loudspeaker coil. Optical path delay element 80 may be displacedwith a predetermined periodic velocity profile (such as a sine wave, sawtooth, or arbitrary waveform though the distance over which optical pathdelay element 80 must be sufficient to detennine the position of imagerplane 18.

In operation, the first and second non-coherent light signals travelingalong single mode optical fibers 68 and 74, respectively, are reflectedback to 2×2 optical coupler 66 (as the reference signal and the delaysignal, respectively) where they recombine and interfere with each otherto form a non-coherent light interference signal. A portion of therecombined reference signal and delay signal is directed into aphotodetector 86 by a single mode optical fiber 87. The analog output ofphotodetector 86 is amplified and filtered by an electronic module 88,and then sampled, digitized, and analyzed by computer 38.

Note that a first and second branch of non-coherent light interferometer36 is defined as the respective path lengths between the location atwhich 2×2 optical coupler 66 splits the light signal into two beams andthe location at which the two beams are recombined and made to interferewith each other. In FIG. 6, the first branch is referred to as thestationary branch while the second branch is referred to as the movablebranch.

In typical operation, the coherent light interference signal is utilizedto sample the non-coherent light interference signal at constantintervals of common variable optical path delay element 80'sdisplacement. Applicants note that alternative configurations fornon-coherent light interferometric measurement apparatus 21 arepossible. For example, a constant velocity common variable optical pathdelay element may replace coherent light interferometer 55.Alternatively, non-coherent light interferometer 36 may not have astationary reference branch. Further, the two branches may be arrangedsuch that the path length of one branch increases while the path lengthof the second branch decreases by a corresponding amount, as illustratedin FIG. 7. As illustrated, a mirror 78' is mounted on common variableoptical path delay element 80. In each alternative configuration, thefunction of the common variable path delay element is to provide arelative path delay between the two branches of the non-coherent lightinterferometer.

The reflections shown in FIG. 8 further explain the interferogramillustrated in FIG. 9. FIG. 9 shows an optimized interferogram obtainedduring a measurement of a digital camera's imager plane location. Duringalignment of the optical probe, the interference signal is optimizedwhen the peak amplitudes of the interferogram are at a maximum.Reflections occur at each optical interface in the focal region ofoptical probe 42, that is, the locations of pellicle 48, the front 52and back 54 surface of plate 20, and at imager plane 18. Theinterferogram measures optical path, so the apparent depth between frontsurface 52 and back surface 54 is a value of nt.

FIG. 10 illustrates locations wherein constructive interference willoccur during the measurement of the imager plane location. A series ofreflections are observed as the variable optical path delay element ismoved. Traces (a)-(j) show the optical signals input into the twobranches of the non-coherent light interferometer. Traces (b)-(j) showdistance delayed traces in the second branch or movable branch of thenon-coherent light interferometer (that is, the second non-coherentlight signal) as the optical path difference between the two branches ofthe non-coherent light interferometer monitonically increases from leftto right. Trace (a) shows the first non-coherent light signal which canbe considered to be the locations of the reflections observed in thestationary reference branch of non-coherent light interferometer 36. Thevertical dashed lines in FIG. 10 emanating from positions of opticalreflections in the stationary reference branch of non-coherent lightinterferometer 36 and represent reference markers where constructiveinterference will occur. Constructive interference will occur when thepulse trains of the two branches have peaks which are aligned verticallyas illustrated. The nine locations of constructive interference shown inTraces (b)-(j) are sequential and define the zero path delay condition(Trace f) and the closest four surrounding locations of constructiveinterference. These locations are symmetrical around the zero path delaycondition. Trace (b) of FIG. 10 illustrates the constructiveinterference wherein common variable optical path delay element 80 is ata position -PG_(depth), and pellicle 48 interferes with the reflectionfrom front surface 52 of plate 20. Similarly, Trace (c) illustrates theconstructive interference wherein common variable optical path delayelement 80 is at a position -(GS_(depth) +nt) and front surface 52 ofplate 20 interferes with the reflection from imager plane 18.Correspondingly, in Trace (d), constructive interference occurs whencommon variable optical path delay element 80 is at a position -(nt) andfront surface 52 of plate 20 interferes with back surface 54 of plate20. Trace (e) shows the location of constructive interference atlocation -GS_(depth) in which back surface 54 of plate 20 interfereswith imager plane 18. Trace (f) shows the condition of zero path delayin which all reflections from the two branches of the non-coherent lightinterferometer constructively interfere with each other. This results inthe largest intensity amplitude peak of the interferogram as illustratedin FIG. 9. Continuing to increase the optical path delay of the secondbranch of the non-coherent light interferometer results in Traces(g)--)j) occurring at+GS_(depth),+nt,+GS_(depth) +nt and PG_(depth)respectively. These locations are symmetric with respect to the zeropath delay condition and are due to the same set of reflections buttraveling down opposite branches of the non-coherent lightinterferometer than those in Traces (b)-(e). The autocorrelationspectrum is in general symmetrical about the origin.

In FIG. 9, the large peak at the left of the figure is the selfcorrelation peak at the location where the path difference between thetwo branches in the non-coherent light interferometer equals zero. Thefirst set of doublets (moving from left to right in FIG. 8) is due tointerstice 22 (i.e., the gap between back surface 54 of plate 20 andimager plane 18) and the optical path of plate 20 (nt), respectively.The second set of doublets (continuing to the right in FIG. 9) occurswhen the path difference between the two branches in the non-coherentlight interferometer equals GS_(depth) +nt and PG_(depth), respectively.Intermediate the second and third set of doublets, motor 82 changesdirections and the third set of doublets is due to PG_(depth) andGS_(depth) +nt respectively. The fourth set of doublets is due to nt andGS_(depth), respectively. After the fourth set of doublets theinterferometer crosses the zero path delay condition, resulting in thesecond large peak. After passing the zero path delay location, motor 82is made to switch directions again and another zero path delay peakoccurs (the third large peak from the left of FIG. 9). The pattern thenrepeats in the right-hand side of the figure. Accordingly, from thisinterferogram, the following information can be determined: the depthfrom the reference surface to front surface 52 of plate 20, the opticalthickness of plate 20, and the depth from back surface 54 of plate 20 toimager plane 18.

In a preferred embodiment, measurements are performed at 20 Hz, thereference surface is selected as lens mount 14 (i.e., Reference PlaneA), and, in a particular camera body 15, the focal depth F_(depth) ofthe lens from the reference surface is determined to be 44 mm. The valueof Delta, dependent on the thickness and index of refraction of plate20, is determined to be between 242.5-277.1 microns for a glass platehaving an index of refraction of 1.5174 and a thickness of about 30 mils+/-2 mils. Accordingly, the in-focus position F_(I) of imager plane 18relative to lens mount surface 14, accounting for optically transparentplate 20, varies between about 44.2425 to about 44.2771 mm. Pellicle 48of a 1.5 μm polyester film is mounted to optical probe assembly 24 so asto be located 40 mm relative to lens mount 14 when optical probeassembly is locked to digital camera body 18. Optical probe assembly 24is removably mounted to digital camera body 18. A one-second measurementtime is standard, and data for twenty measurement cycles are typicallycalculated. Applicants have noted that the measurement reproducibilityfor fifty mount/dismount measurement cycles has been better than 2.5microns for the measurement of the actual depth of the imager planerelative to the reference surface.

A corresponding non-coherent light interferometer 36 having a standardmode configuration is illustrated in FIG. 11. In this configuration, theoptical probe assembly is inserted into one of the interfering branchesof the non-coherent light interferometer, thus requiring the length ofoptical fiber 26 to be substantially equal to optical fiber 74.

The apparatus of the present invention may be employed in severalmethods: (i) to determine the position of an imager plane of an imagersensor within a camera body, (ii) verify that the position of an imagerplane of an image sensor is within a desired tolerance, such as in-focusposition F_(I), (iii) determine the difference between the currentposition of the imager plane and the desired position of the imagerplane, and, optionally, moving the imager plane to the desired position,and (iv) to position the imager plane at a desired position. Translationmeans, either manual or mechanical, may be employed to align the imagerplane to the desired position. Such translation means are well known tothose skilled in the art.

As indicated above, non-coherent light interferometry may be employed inseveral ways to these methods: in a standard mode configuration, and inan autocorrelation mode. FIGS. 12 and 13 illustrate a method flow chartincorporating an autocorrelation mode configuration, while FIG. 14illustrates a method flow chart incorporating a standard modeconfiguration of a non-coherent light interferometer. In each methodillustrated in FIGS. 12 and 13, the apparatus of the present inventionis employed to determine the position of the imager plane within acamera body (i.e., method (i) above). FIG. 12 illustrates a methodincorporating an interferometer having a stationary and movable branchcontrollable by common variable optical path delay element 80. FIG. 13illustrates a method incorporating an interferometer wherein commonvariable optical path delay element 80 causes the path length of thefirst branch to increase in length while the path length of the secondbranch to decrease by a corresponding amount.

As illustrated in FIG. 12 (an autocorrelation mode configuration),optical probe assembly 24 is mounted and locked to camera body 15 (step200). Non-coherent light source 30 emits a continuous wave non-coherentlight signal incident on optical probe assembly 24 (step 202). A portionof the non-coherent light signal is transmitted through pellicle 48(step 204) to imager plane 18 (step 206). A portion of the non-coherentlight signal is reflected by pellicle 48, front surface 52, back surface54, and imager plane 18 (step 208). These reflected signals arecollected (step 210) and divided into a first and second light signals(step 212). The first light signal is applied to stationary referencereflector 70 (step 214) wherein a portion of the first light signal isreflected by stationary reference reflector 70 to form a referencesignal which is collected (step 216). The second light signal is appliedto variable optical path delay element 80 to form a delay signal (step218) which is collected (step 220). This application of the second lightsignal to the variable optical path delay element causes the opticalpath length of the second light signal to be varied when the variableoptical path delay element is displaced with a predetermined distance orvelocity profile (step 222). The delay signal and the reference signalare combined to form a non-coherent light interference signal (step 224)which is collected (step 226). The interference signal is analyzed (step228) to determine the depth from the reference surface to front surface52 of plate 20, the optical thickness of optically transparent plate 20,and the depth from back surface 54 of plate 20 to imager plane 18 (step230). From this information, the position of imager plane 18 relative tothe reference surface can be calculated (step 232).

To analyze the non-coherent light interference signal (step 228), thenon-coherent light interference signal is sampled, digitized, and storedin a data array. The stored array is then analyzed to determine thedepth from the reference surface to front surface 52, the opticalthickness of optically transparent plate 20, and the depth from backsurface 54 to imager plane 18. From these values, the position of theimage sensor relative to the reference surface can be determined usingEquation 1. Knowing the focal depth of the camera lens, the differencebetween the position of the image sensor and the in-focus position canbe determined, whereby image sensor 16 can be moved by the differencevalue to locate the imager plane at the in-focus position.

As illustrated in FIG. 13 (an autocorrelation mode configuration),optical probe assembly 24 is mounted and locked to camera body 15 (step250). Non-coherent light source 30 emits a continuous wave non-coherentlight signal incident on optical probe assembly 24 (step 252). A portionof the non-coherent light signal is transmitted through pelicle 48 (step254) to imager plane 18 (step 256). A portion of the non-coherent lightsignal is reflected by pellicle 48, front surface 52, back surface 54,and imager plane 18 (step 258). These reflected signals are collected(step 260) and divided into a first and second light signals (step 262).The first and second light signals are applied to variable optical pathdelay element 80 (step 264) to form first and second delay signals,respectively, (step 266). This application of the first and second lightsignals to the variable optical path delay element causes the opticalpath lengths to be varied when the variable optical path delay elementis displaced with a predetermined distance or velocity profile (step268). The first and second delay signals are combined to form anon-coherent light interference signal (step 270) which is collected(step 272). The interference signal is analyzed (step 274) to determinethe depth from the reference surface to front surface 52 of plate 20,the optical thickness of optically transparent plate 20, and the depthfrom back surface 54 of plate 20 to imager plane 18 (step 276). Fromthis information, the position of imager plane 18 relative to thereference surface can be calculated (step 278).

To analyze the non-coherent light interference signal (step 274), thenon-coherent light interference signal is sampled, digitized, and storedin a data array. The stored array is then analyzed to detennine thedepth from the reference surface to front surface 52, the opticalthickness of optically transparent plate 20, and the depth from backsurface 54 to imager plane 18. From these values, the position of theimage sensor relative to the reference surface can be determined usingEquation 1. Knowing the focal depth of the camera lens, the differencebetween the position of the image sensor and the in-focus position canbe determined, whereby image sensor 16 can be moved by the differencevalue to locate the imager plane at the in-focus position.

FIG. 14 illustrates a method incorporating the standard modeconfiguration. Optical probe assembly 24 is mounted and locked to camerabody 15 (step 300). Non-coherent light source 30 emits a non-coherentlight signal incident on 2×2 optical coupler 66 (step 302) which isdivided into a first and second non-coherent light signal (step 304)traveling along optical fibers 26 and 74, respectively. The firstnon-coherent light signal is transmitted through pellicle 48 (step 306)to imager plane 18 of image sensor 16 (step 308). A portion of the firstnon-coherent light signal is reflected by pellicle 48, front surface 52,back surface 54, and imager plane 18 (step 310). These reflected signalsare collected and form an object signal (step 312). The secondnon-coherent light signal is applied to variable optical path delayelement 80, forming a delay signal (step 314), which is collected (step316). Optical path delay element 80 is displaced (step 318), and thedelay signal and object signal are combined to form a non-coherentinterference signal (step 320). The corresponding interference signal isanalyzed (step 322) to determine the values of the depth from thereference surface to front surface 52, the optical thickness ofoptically transparent plate 20, and the depth from back surface 54 toimager plane 18 (step 326). From this information, the position ofimager plane 18 relative to the reference surface can be calculated(step 328).

To analyze the non-coherent light interference signal (step 324), thenon-coherent light interference signal is sampled, digitized, and storedin a data array. The stored array is then analyzed to determine thedepth from the reference surface to front surface 52, the opticalthickness of optically transparent plate 20, and the depth from backsurface 54 to imager plane 18. From these values, the position of theimage sensor relative to the reference surface can be determined usingEquation 1. Knowing the focal depth, the difference between the positionof the image sensor and the focal depth can be determined, whereby imagesensor 16 can be moved by the difference value to locate the imagerplane at the in-focus position.

Additional steps may be required to accomplish the other methodsdescribed above. Specifically, to verify that the position of an imagerplane of an image sensor is within a desired tolerance (i.e., method(ii) above), an additional calculation step of determining whether theposition of the imager plane is within the desired tolerance isrequired. To determine the difference between the current position ofthe imager plane and the desired position of the imager plane (i.e.,method (iii) above), an additional calculation step of Equation 6 isemployed. to position the imager plane at a desired position (i.e.,method (iv) above), the difference between the current position and thedesired position of the imager plane is determined, and means areprovided to move the imager plane by the difference.

While the above discussion refers to a single measurement location, aplurality of locations on the surface of image sensor 16 may be measuredto provide (a) an indication of parallelism of imager plane 18 withrespect to a reference surface and/or plate 20, and (b) a measure of thedegree of flatness or bowing of imager plane 18, thereby providingspatial information about the focal position of the image sensor. Forexample, FIG. 15 illustrates the use of a 1×N optical switch 120,configured as a 1:5 optical switch, which allows five locations to bemeasured by means of a five measurement location fixture containing fiveindividual optical probes mounted in a single optical probe assembly.The depth direction is defined as the z-axis. Each of the fivemeasurement locations in the x,y plane (i.e., the locations of each ofthe optical probes) are measured sequentially using optical switch 120.Operation of the multiple-location measurement apparatus is similar tothe single-location measurement apparatus described above with referenceto FIGS. 12-14. However, the measurement process is repeated for eachlocation. For example, in the instant case the measurement would berepeated five times with a switch being toggled to each of theindividual five measurement locations. Additional information isprovided about the flatness of the focal plane of the image sensor, theparallelism of imager plane 18 to plate 20 and the reference surface,the thickness of uniformity of plate 20, and the uniformity ofinterstice 22. A minimum of three measurement locations is required toobtain information about the parallelism of the imager plane relative tothe reference surface.

An example of data obtained at five measurement locations for a digitalimager is provided in Table I. Columns 1 and 2 of Table I identify the xand y locations of five measured positions utilizing the apparatus ofFIG. 15. Columns 3 through 5 show the measured parameters from theinterferograms shown in FIG. 9. (FIG. 9 shows the interferogram obtainedat measurement location (0,0) for this particular camera.) Column 6shows the values of D_(actual) calculated using Equation 3; Column 7shows the values of Delta obtained from Equation 2; and Column 8 showsthe values for focus error D_(F) calculated using Equation 6. The lowerportion of Table I summarizes the measurement statistics. The range ofthe depth from the pellicle to the front surface of plate 20 along thez-axis is observed to be only 0.34 microns, implying a high degree ofparallelism of the pellicle to the front surface of plate 20. Theoptical thickness (i.e., nt) of plate 20 varied by 2.78 microns which isequal to a thickness variation of 1.83 microns over the measured region.The interstice varied by 3.92 microns, and the digital imager planefocus error varied from 14.93-20.13 microns over the measured surface ofthe imager plane. Hence, the imager plane of the digital camera measuredin Table I is not exactly parallel to the reference surface of thecamera. Rather, some variation occurs along the x and y axis, with themajority being along the x axis. The flatness of the imager plane canalso be determined from the data in Table I; the data in Table Iindicates that the image sensor has a relatively flat imager plane.

                  TABLE I                                                         ______________________________________                                        Five position measurement data on a digital camera                            utilizing the apparatus and method of the present invention                   x   y      GS.sub.depth                                                                          plate nt                                                                             PG.sub.depth                                                                        D.sub.actual                                                                         Delta  D.sub.F                         ______________________________________                                        -9  -6     1050.55 1223.52                                                                              2433.38                                                                             44290.26                                                                             274.94 15.32                           -9  6      1050.58 1223.24                                                                              2433.08                                                                             44289.80                                                                             274.88 14.93                           0   0      1052.51 1224.61                                                                              2433.27                                                                             44292.82                                                                             275.18 17.64                           9   -6     1054.47 1225.48                                                                              2433.42                                                                             44295.51                                                                             275.38 20.13                           9   6      1054.45 1226.02                                                                              2433.19                                                                             44295.61                                                                             275.50 20.11                           AVG    1052.51 1224.57  2433.27                                                                             44292.80                                                                             275.18 17.62                             sigma  1.95    1.20     0.14  2.77   0.27   2.50                              max    1054.47 1226.02  2433.42                                                                             44295.61                                                                             275.50 20.13                             min    1050.55 1223.24  2433.08                                                                             44289.80                                                                             274.88 14.93                             range  3.92    2.78     0.34  5.81   0.62   5.20                              ______________________________________                                    

While additional measurement locations may be measured utilizing a 1×Noptical switch, Applicants have noted that increasing the number densityof measurement points constrains the size of the optical elementsutilized for alignment. As such, an optional translation stage (notshown) movable in two dimensions (for example, an x,y coordinatesystem), may be mounted to optical probe assembly 24. Such a translationstage allows multiple measurements on the image sensor to be made usinga single measurement apparatus, thereby providing an alternative tomultiplexing as illustrated in FIG. 15.

The invention has been described in detail with particular reference toa presently preferred embodiment, but it will be understood thatvariations and modifications can be effected within the spirit and scopeof the invention. For example, the invention could be utilized tomeasure the position of another optical component, such as a filter. Thepresently disclosed embodiments are therefore considered in all respectsto be illustrative and not restrictive. The scope of the invention isindicated by the appended claims, and all changes that come within themeaning and range of equivalents thereof are intended to be embracedtherein.

Parts List

10 conventional camera body

12 lens

13 film

14 lens mount

15 digital camera body

16 image sensor; CCD

18 imager plane of image sensor

20 optically transparent plate; glass plate

21 non-coherent light interferometric measurement apparatus

22 interstice

23 locking means; spring loaded locking pin

24 optical probe assembly

25 unlocking means; spring loaded release pin

26 single mode fiber

28 1×2 optical coupler

30 non-coherent light source

32 single mode fiber

34 optical fiber

36 non-coherent light interferometer

38 computing means; computer

40 probe mounting surface

42 optical probe; collimating lens, fiber collimator

43 probe housing

44 probe assembly mounting means

45 probe assembly gripping means

46 probe recess

48 pellicle

49 pellicle mount

50 O-ring

52 front surface of plate 20

54 back surface of plate 20

55 coherent light interferometer

56 coherent light source; laser

58 splitting means; beam splitter

60 stationary retroreflector

62 optical element; retroreflector

64 photodetector

65 signal processing electronics

66 2×2 optical coupler

68 single mode optical fiber

70 stationary reference reflector

72 collimating applying and collecting means

74 single mode optical fiber

76 collimating applying and collecting means

78 mirror

80 common variable optical path delay element

82 motor

84 motor drive control electronic module

86 photodetector

87 single mode optical fiber

88 electronic module

92 fiber collimator collar

94 adjustment collar

96 adjustment screw(s)

98 ball pivot

100 ball pivot receiving plate

102 opening

104 mounting plate

106 fiber collimator collar mounting means

108 ball pivot receiving plate mounting means

110 optical probe assembly means

112 recess

114 collimating lens orientation and locking means

116 access holes

120 optical switch

What is Claimed is:
 1. An apparatus for determining a position of animage sensor in a digital camera relative to a reference surface on saiddigital camera, said image sensor including (i) an imager plane and (ii)an optically transparent plate having a front surface and a backsurface, said plate being spaced from said imager plane, comprising:anoptical probe assembly adapted to be removably mountable to the digitalcamera and lockable in a predetermined orientation relative to thedigital camera, said optical probe assembly including (a) an opticalprobe, and (b) a pellicle securely mounted relative to said opticalprobe, said pellicle disposed intermediate said reference surface andsaid imager plane, said pellicle disposed at a first depth from saidreference surface when said optical probe is in said locked orientation,said optically transparent plate disposed intermediate said imager planeand said pellicle, a non-coherent light interferometer and anon-coherent light source in communication with said optical probe bymeans of an optical coupler; and means for determining (i) a seconddepth from said reference surface to said optically transparent platefront surface, (ii) an optical thickness of said optically transparentplate, and (iii) a third depth from said optically transparent plateback surface to said imager plane.
 2. The apparatus according to claim 1wherein said optical probe assembly further comprises a ball pivot, andsaid optical probe is rotatably mounted within said ball pivot.
 3. Theapparatus according to claim 1 wherein said optical probe assemblyincludes an adjustment means for optimizing a non-coherent lightinterference signal from said non-coherent light interferometer.
 4. Theapparatus according to claim 1 wherein said optical probe assemblyincludes an adjustment means for orienting the axis of said opticalprobe normal to said reference surface.
 5. The apparatus according toclaim 1 wherein said optical probe is a collimating lens pigtailed to asingle mode optical fiber, and said optical probe assembly furthercomprises mounting means, orientation and locking means, and grippingmeans.
 6. An apparatus for positioning an image sensor in a digitalcamera relative to an in-focus position, said image sensor including (i)an imager plane and (ii) an optically transparent plate having a frontsurface and a back surface, said plate being spaced from said imagerplane, comprising:an optical probe adapted to be removably mountable tothe digital camera and lockable in a predetermined orientation relativeto the digital camera; a pellicle rigidly mounted to said optical probe,said pellicle disposed intermediate said reference surface and saidimager plane, said pellicle disposed at a first depth from saidreference surface when said optical probe is in said locked orientation,said optically transparent plate disposed intermediate said imager planeand said pellicle; a non-coherent light interferometer and anon-coherent light source in communication with said optical probe bymeans of an optical coupler; means for determining (i) a second depthfrom said reference surface to said optically transparent plate frontsurface, (ii) an optical thickness of said optically transparent plate,and (iii) a third depth from said optically transparent plate backsurface to said imager plane, (iv) a position of the imager planerelative to the in-focus position; and translation means for aligningsaid imager plane at the in-focus position.
 7. An apparatus fordetermining a position of an image sensor mounted in a digital camerarelative to a reference surface on said digital camera, said imagesensor including (i) an imager plane and (ii) an optically transparentplate having a front surface and a back surface, said plate being spacedfrom said imager plane, comprising:an optical probe assembly adapted tobe removably mountable to the digital camera and lockable in apredetermined orientation relative to the digital camera, said opticalprobe assembly including (a) a plurality of optical probes, and (b) apellicle securely mounted relative to each of said plurality of opticalprobes, said pellicle disposed intermediate said reference surface andsaid imager plane, said pellicle disposed at a first depth from saidreference surface when said optical probes are in said lockedorientation, said optically transparent plate disposed intermediate saidimager plane and said pellicle; a non-coherent light interferometer anda non-coherent light source in communication with said optical probes bymeans of an optical coupler; optical switching means; and means fordetermining, for each of said plurality of optical probes, (i) a seconddepth from said reference surface to said optically transparent platefront surface, (ii) an optical thickness of said optically transparentplate, and (iii) a third depth from said optically transparent plateback surface to said imager plane.
 8. An apparatus for determining aposition of an image sensor mounted in a digital camera relative to areference surface on said digital camera, said image sensor including(i) an imager plane and (ii) an optically transparent plate having afront surface and a back surface, said plate being spaced from saidimager plane, comprising:an optical probe assembly adapted to beremovably mountable to the digital camera and lockable in apredetermined orientation relative to the digital camera, said opticalprobe assembly including (a) an optical probe, and (b) a pelliclesecurely mounted relative to said optical probe, said pellicle disposedintermediate said reference surface and said imager plane, said pellicledisposed at a first depth from said reference surface when said opticalprobe is in said locked orientation, said optically transparent platedisposed intermediate said imager plane and said pellicle, anon-coherent light interferometer and a non-coherent light source incommunication with said optical probe by means of an optical coupler;translation means for moving said optical probe along an axis normal tosaid reference surface to provide a plurality of measurement locations;and means for determining, at each of said plurality of measurementlocations, (i) a second depth from said reference surface to saidoptically transparent plate front surface, (ii) an optical thickness ofsaid optically transparent plate, and (iii) a third depth from saidoptically transparent plate back surface to said imager plane.
 9. Anapparatus for determining whether an image sensor mounted in a digitalcamera is parallel relative to a reference surface on said digitalcamera, said image sensor including (i) an imager plane and (ii) anoptically transparent plate having a front surface and a back surface,said plate being spaced from said imager plane, comprising:an opticalprobe assembly adapted to be removably mountable to the digital cameraand lockable in a predetermined orientation relative to the digitalcamera, said optical probe assembly including (a) a plurality of opticalprobes, and (b) a pellicle securely mounted relative to each of saidplurality of optical probes, said pellicle disposed intermediate saidreference surface and said imager plane, said pellicle disposed at afirst depth from said reference surface when said optical probes are insaid locked orientation, said optically transparent plate disposedintermediate said imager plane and said pellicle; a non-coherent lightinterferometer and a non-coherent light source in communication withsaid optical probes by means of an optical coupler; optical switchingmeans; and means for determining, for each of said plurality of opticalprobes, (i) a second depth from said reference surface to said opticallytransparent plate front surface, (ii) an optical thickness of saidoptically transparent plate, and (iii) a third depth from said opticallytransparent plate back surface to said imager plane.
 10. An apparatusfor determining whether an image sensor mounted in a digital camera isparallel relative to a reference surface on said digital camera, saidimage sensor including (i) an imager plane and (ii) an opticallytransparent plate having a front surface and a back surface, said platebeing spaced from said imager plane, comprising:an optical probeassembly adapted to be removably mountable to the digital camera andlockable in a predetermined orientation relative to the digital camera,said optical probe assembly including (a) an optical probe, and (b) apellicle securely mounted to said optical probe, said pellicle disposedintermediate said reference surface and said imager plane, said pellicledisposed at a first depth from said reference surface when said opticalprobe is in said locked orientation, said optically transparent platedisposed intermediate said imager plane and said pellicle; anon-coherent light interferometer and a non-coherent light source incommunication with said optical probe by means of an optical coupler;optical switching means; and means for determining (i) a second depthfrom said reference surface to said optically transparent plate frontsurface, (ii) an optical thickness of said optically transparent plate,and (iii) a third depth from said optically transparent plate backsurface to said imager plane.
 11. An apparatus for determining thedegree of flatness of an image sensor mounted in a digital camera, saidimage sensor including (i) an imager plane and (ii) an opticallytransparent plate having a front surface and a back surface, said platebeing spaced from said imager plane, comprising:an optical probeassembly adapted to be removably mountable to the digital camera andlockable in a predetermined orientation relative to the digital camera,said optical probe assembly including (a) a plurality of optical probes,and (b) a pellicle securely mounted relative to each of said pluralityof optical probes, said pellicle disposed intermediate said referencesurface and said imager plane, said pellicle disposed at a first depthfrom said reference surface when said plurality of optical probes are insaid locked orientation, said optically transparent plate disposedintermediate said imager plane and said pellicle; a non-coherent lightinterferometer and a non-coherent light source in communication withsaid optical probes by means of an optical coupler; optical switchingmeans; and means for determining, for each of said plurality of opticalprobes, (i) a second depth from said reference surface to said opticallytransparent plate front surface, (ii) an optical thickness of saidoptically transparent plate, and (iii) a third depth from said opticallytransparent plate back surface to said imager plane.
 12. An apparatusfor determining the degree of flatness of an image sensor mounted in adigital camera, said image sensor including (i) an imager plane and (ii)an optically transparent plate having a front surface and a backsurface, said plate being spaced from said imager plane, comprising:anoptical probe assembly adapted to be removably mountable to the digitalcamera and lockable in a predetermined orientation relative to thedigital camera, said optical probe assembly including (a) an opticalprobe, and (b) a pellicle securely mounted relative to said opticalprobe, said pellicle disposed intermediate said reference surface andsaid imager plane, said pellicle disposed at a first depth from saidreference surface when said optical probe is in said locked orientation,said optically transparent plate disposed intermediate said imager planeand said pellicle; a non-coherent light interferometer and anon-coherent light source in communication with said optical probe bymeans of an optical coupler; optical switching means; and means fordetermining (i) a second depth from said reference surface to saidoptically transparent plate front surface, (ii) an optical thickness ofsaid optically transparent plate, and (iii) a third depth from saidoptically transparent plate back surface to said imager plane.